The US Supreme Court is being asked to block tonight's scheduled execution of Texas death row inmate Derrick Sean O'Brien.
Prosecutors say the street gang member faces execution over the 1993 torture killing of two Houston girls.
Fourteen-year-old Jennifer Ertman and 16-year-old Elizabeth Pena were strangled.
O'Brien -- who's now 31 -- was one of six gang members convicted in the slayings. He's the first to face lethal injection over the deaths.
O'Brien would be the 14th condemned killer in Texas to have his punishment carried out this year.
The defense argues there's no legal procedure allowing condemned Texas prisoners to raise challenges that drugs used in lethal injections could cause unconstitutional pain.
O'Brien has declined to speak with reporters about his pending execution.